This application claims the priority of German Application No. 101 26 469.0-35, filed May 31, 2001, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a slot antenna element in the form of a rectangular waveguide.
Slot antenna elements, frequently used as antennas in high-frequency engineering applications, comprise a waveguide which extends in a longitudinal direction and has at least one slot for the emission of a portion of an electromagnetic wave guided in the waveguide. In the area of the slot, a pin consisting of a conductive material is often provided as a device for exciting the emission of the waveguide wave from the slot. Such a slot antenna is known, for example, from German patent document DE-GM 1 959 159. In the equivalent circuit diagram, this pin is represented by a first shunt-connected positive capacitance C1 at the waveguide.
However, from German patent document DE 33 10 531 A1, slot antenna elements are also known, in which case the waveguide is frequently provided with a ridge extending on the inside at the wall opposite the slot in the longitudinal direction of the waveguide.
In the special case of a symmetrically constructed rectangular ridge waveguide (in which a slot extending in the longitudinal direction of the waveguide as well as a ridge are arranged in the center with respect to the cross dimension of the waveguide), the above-mentioned pin made of a conductive material is a necessary means for exciting the emission of the waveguide wave from the slot. The operating principle consists of an asymmetrical distortion of the field distribution in the waveguide under the slot. In the equivalent circuit diagram, the slot-pin combination acts like a shunt-connected capacitor in parallel to a series-resonant circuit. For the compensation of the capacitor, an inductive diaphragm can be used in waveguide technique. However, its implementation is difficult in practice and furthermore itself causes a field distortion counterproductive to the excitation of the emission.
It is an advantage of the invention to provide an improved slot antenna element.
According to the invention, this advantage is achieved by providing a slot antenna element in the form of a rectangular waveguide. The slot antenna element includes at least one slot situated in the center of one broad side, a rectangular ridge arranged in the center of the interior surface of the other broad side. The slot and the ridge each extend along the longitudinal direction of the waveguide. A coupling device, particularly in the form of a pin, is arranged in the area of the slot, which excites the slot to emit electromagnetic energy, and a compensation device is constructed on the surface of the ridge facing the slot, which compensation device compensates the mismatch of the waveguide caused by the coupling device with respect to the generator feeding the waveguide with electromagnetic energy. The compensation device is constructed such that the ridge has a step-shaped indentation in the area of the slot. Advantageous further developments of the slot antenna element according to the invention are the object of dependent claims.
According to the invention, the slot antenna element in the form of a rectangular waveguide comprises:
a) at least one slot situated in the center of one broad side,
b) a rectangular ridge arranged in the center of the interior surface of the other broad side, the slot and the ridge each extending along the longitudinal direction of the waveguide,
c) coupling devices, particularly a pin, arranged in the area of the slot, which excite the slot to emit electromagnetic energy, and
d) compensation devices constructed on the surface of the ridge facing the slot, which compensation devices compensate the mismatch of the waveguide caused by the coupling devices with respect to the generator feeding the waveguide with electromagnetic energy, the compensation devices being constructed such that the ridge has a step-shaped indentation in the area of the slot.
In an equivalent circuit representation, in which the slot of the waveguide is illustrated as a series-resonant circuit, the step-shaped indentation preferably represents a negative capacitance C2 connected in parallel with respect to the series-resonant circuit.
The negative and the positive capacitance can be explained by means of field theory. Thus, the coupling device in the area of the slot represents a positive capacitance. Field-theoretically, the effect of the coupling device can be explained as a field distortion, predominantly of the electric field of the line. This results in an increase of the electric field energy around the coupling device, for example, a pin. In an equivalent circuit representation, this effect can be represented as a capacitance. Since the concentration of the electric field is increased, the capacitance is positive.
The ridge on the broad side of the waveguide opposite the slot can also be represented as a capacitance in an equivalent circuit. As a result of the step-shaped indentation of the ridge according to the invention, the ridge size is reduced. This causes a lowering of the electric field energy relative to a full size ridge. The capacitance therefore has a negative value.
According to a preferred embodiment of the invention, the devices for exciting the emission of the waveguide wave are formed by a pin made of a conductive material arranged laterally next to the slot.
With respect to the longitudinal direction of the waveguide, the pin is preferably arranged at the level of the center of the slot.
In a preferred embodiment, the step-shaped indentation has a rectangular cross-section of a length D and a height H parallel and/or perpendicular to the longitudinal direction of the ridge. The length D and the height H of the step-shaped indentation are preferably selected such that C1+C2=0 applies, wherein C1 indicates the coupling devices to be represented as the capacitance C1 in an equivalent circuit, and C2 indicates the step-shaped indentation in the ridge to be represented as a negative capacitance C2 in an equivalent circuit.
The step-shaped indentation and the slot are preferably arranged with respect to the longitudinal direction of the waveguide in the center relative to one another.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.